There has been some renewed interest in recent years in disorders of olfaction. Decreased sense of smell can lead to significant impairment of quality of life, including taste disturbance and loss of pleasure from eating with resulting changes in weight and difficulty in avoiding health risks such as spoiled food or leaking natural gas. Recent epidemiological reports have shown that despite fairly low self-reported prevalence of these disorders in large population studies, when validated smell identification or threshold tests are used, they reveal quite a high prevalence of hyposmia and anosmia in certain groups, especially the elderly. Several different pathophysiologic processes, such as head trauma, aging, autoimmunity, and toxic exposures, can contribute to smell impairment, with distinct implications concerning prognosis and possible treatment. As allergists, we are most likely to see this symptom in patients with chronic rhinosinusitis, and this now appears to be due more to the mucosal inflammation than to physical airway obstruction.